1. Technical Field
Embodiments of the present invention relate to an image forming apparatus and method that effectively conducts a forcible toner consumption process, in which a latent image formed for forced toner consumption is formed on a latent image bearer to force a developing device to consume degraded toner thereon.
2. Related Art
Conventionally, an image forming apparatus that forms an image by using an electrophotographic process is known. Specifically, after a latent image bearer such as a photoconductive drum, etc., is uniformly charged, an electrostatic latent image is formed thereon that is then developed by a developing device to obtain a toner image. The toner image is then transferred onto a recording medium (a recording sheet) from the latent image bearer either directly or indirectly via an intermediate transfer member.
In such a conventional system, when multiple images each having a low image area ratio are continuously formed for a long time, some toner in the developing device is only stirred without being consumed at the time. With this, additives either separate from or are embedded in surfaces of toner particles, thereby accelerating degradation of the toner. As degradation of the toner progresses, degradation of image quality also occurs simultaneously due to defective transfer, thereby generating a poor image, such as a scumming image (an image with toner adhering to a blank area), a void image, etc.
To suppress generation of such a poor image, a conventional image forming apparatus usually conducts a forcible toner consumption process. Specifically, when an image area ratio of an image having been most recently developed and outputted falls below a predetermined threshold, a toner image is formed on the photoconductive drum in a region thereof that corresponds to an interval between successive sheets of recording media (herein after sometimes simply referred to as a sheet interval corresponding region) using an amount of toner corresponding to a decreased level of the image area ratio to forcibly consume such toner in the developing device. Hence, by promoting consumption of the old toner and replacement with new toner in the developing device and thereby reducing a percentage of deteriorated toner in the developing device, generation of a poor image possibly caused by the degraded toner can be suppressed. Out of all region of the photoconductive drum in a circumferential direction thereof, the sheet interval corresponding region corresponds to an interval between successive sheets of recording media sent in a continuous printing mode to a transfer station.
In such a conventional image forming apparatus, the toner image is formed on the photoconductive drum and a drum cleaning unit is disposed surrounding the photoconductive drum to remove the toner from the photoconductive drum. However, the drum cleaning unit is there simply to clean the photoconductive drum by removing transfer residual toner that remains on the photosensitive surface in a toner image transfer process. Further, since an amount of toner in a toner image before the toner transfer process is far greater than an amount of toner remaining after the toner transfer process, the drum cleaning unit generally cannot remove all of the toner in the toner image formed for forced consumption alone. In particular, like in the former conventional image forming apparatus, since four photoconductive drums are disposed side by side to separately form yellow (Y), magenta (M), cyan (C), and black (K) color toner images, respectively, an individual drum cleaning unit needs to be compact to ease a layout of these drums. When it is attempted to remove all of the toner in the toner image formed for forced consumption only by using such a compact drum cleaning unit alone, various problems more likely arise due to defective cleaning.
According to another conventional image forming apparatus, four latent images formed for forced toner consumption are formed on four photoconductive drums of respective Y, M, C, and K colors and are developed and transferred onto an intermediate transfer belt at different positions thereof as the belt moves. Along with movement of the intermediate transfer belt, these four toner images of Y, M, C, and K colors each formed for forced consumption thereon are sent to a belt cleaning unit at different times from each other and are removed from the intermediate transfer belt.